THE STEM \M> CALYX 



CHAPTER II. 



THE STEM AND CALYX. 



A. The Stem. 



The stem of the Blastoidea is comparatively but little known, since individuals in 

 which the stem remains attached to the calyx are but rarely found preserved. Mr. 

 Wachsmuth informs us that he has a slab of Pentrcmites from the Chester Limestone 

 in which three specimens have stems of between 5 and 8 inches in length ; but we 

 have seen nothing of this kind in any pieces of the Carboniferous Limestone from 

 Bolland and Clitheroe, which are sometimes crowded with stemless cups of Granato- 

 crinus ellipticus. 



The best preserved stem which we have been able to examine is in a specimen of 

 Granatocrwms Nbrwoodi belonging to Mr. "Wachsmuth, which is figured in PI. III. 

 fig. 16. It consists of small, thin, discoidal joints, which have no special distinctive 

 marks. Isolated stem-joints are abundant in every rock which contains Blastoid 

 remains, but there is no test by which the stem-joints of a Blastoid can be distin- 

 guished from those of a Crinoid. No stem has yet been discovered which bears whorls 

 of cirri as in the Pentacrinida? and in some Palaeozoic Crinoids (Hystiricrinus and 

 Belemnoerinus) ; but Mr. Wachsmuth informs us that he has obtained one Pentrc- 

 mites from the Kaskaskia Limestone in which the stem ends below in a branching root 

 like that of the Bourgueticrinidse. Both in this Pentremite and in (Imnatocrinus 

 Nonooodi the stem consists of very numerous discoidal joints, but in Grcmatocrinus 

 Derbiensis it appears to have been composed of more elongated joints, like those of 

 the Bhizocrinus- and Bat/ii/crintis-stems (PI. VI. fig. 23). 



In the British species of Granatocrinus the stem-facet is of moderate size compared 

 to the diameter of the flat basal disc of which it occupies the centre (PI. VIII. 

 figs. 13, 18; PI. IX. figs. 3,4, 9, 13); while in Oropliocrinus, Phamoschisma, 

 Cryptoscliisma, Troostoevinas, and other types with a more or less elongated basal 

 cup, its narrow lower end rests directly upon the first stem-joint, which is sometimes 

 preserved, as in Phcenoschisma Archiaci and Orophocrimts stelUformis (PL XII. fig. 10 ; 

 PI. XVI. fig. 7). 



Three genera of Blastoids — Pentephijlhnn (PI. XVI. fig. 1G), Eleutherocrinus 

 (Fig. II. on p. 14), and Astrocrinus (PI. XX.) — appear to have had no stem in the 

 adult state, whatever may have been the case during early life. The asymmetry of 



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